A semiconductor pressure detection device is provided which is adapted to detect pressure using resistors formed in the surface area of a semiconductor substrate and having a piezo-effect. A diode is formed in the surface area of the semiconductor substrate and a drive voltage corresponding to a temperature variation is supplied to a bridge circuit through the diode.

In a proportioner for proportioning a fluid flow (.phi.) from an input side of a first proportioning element (10) to an output side of a second proportioning element (10), the first and second proportioning elements comprise a membrane (12) provided with at least one opening (16) acting as a flow resistor for a medium to be proportioned, and a pressure sensor (14) integrated in the membrane (12) and used for detecting a pressure difference between the input side and the output side of the proportioning element (10). The proportioner comprises a pressure transducer for input-side application of a pressure to the medium to be proportioned. The first and the second proportioning element (10) are arranged in succession so as to permit, on the basis of the pressure drop across the membranes (12) of the two proportioning elements (10), the detection of clogging or blocking of the respective flow resistor provided in these membranes (12).

An electronic circuit uses a two input operational amplifier for converting a pressure into an electrical signal. The bias potentials at the two inputs are equal to each other in the absence of pressure. The bias potential is applied to one input via a pressure sensitive resistor comprising a semiconductor diaphram with a resistance diffused thereon. When pressure appears, the resistance changes and there is a difference of potential at the two inputs, which is processed into the electrical signal.

A semiconductor transducer has a strain sensitive region, at least one strain gage formed integrally with a major surface of the strain sensitive region corresponding to a major surface of a monocrystalline silicon substrate, a bridge circuit including the strain gage, an operational amplifier, an input terminal of which is connected to an output terminal of the bridge circuit, and parallel-connected resistors which are integrally formed on the major surface of the monocrystalline silicon substrate and each of which has two ends connected to the input terminal and an output terminal of the operational amplifier, respectively, the strain sensitive region, the strain gage, the operational amplifier and the parallel-connected resistors being formed on the monocrystalline silicon substrate, wherein a difference between a temperature coefficient of resistance of the strain gage and a temperature coefficient of sensitivity thereof is set to be substantially the same as a temperature coefficient of resistance of the parallel-connected resistors. Resistors connected in series with the input terminals of the operational amplifier can thus be eliminated. The resistance of the parallel-connected resistors can be decreased, thereby providing a compact, highly integrated arrangement. In addition, a temperature compensator need not be used to compensate for the sensitivity.

In the disclosed measuring system, the strain in opposingly stressed strain gauges is measured by alternately driving currents through the gauges, and measuring the resulting differences in the alternate currents. Two reversely poled transistors, or two FETs, form low impedance switches that alternately drive the currents through the gauges. A constant current source or a resistor provides a current path to both gauges.